Datasheet
TDA7294
3
1
4
137
815
2
14
6
10
R3 680
C11 22µF
L3 5µH
270
R16
13K
C15
22µF
9
R16
13K
C13 10µF
R13 20K
C11 330nF
R15 10K
C14
10µF
R14 30K
D5
1N4148
PLAY
ST-BY
270
L1 1µH
T1
BDX53A
T3
BC394
D3 1N4148
R4
270
R5
270
T4
BC393
T5
BC393
R6
20K
R7
3.3K
C16
1.8nF
R8
3.3K
C17
1.8nF
Z2 3.9V
Z1 3.9V
L2 1µH
270
D4 1N4148
D2 BYW98100
R1
2
R2
2
C9
330nF
C10
330nF
T2
BDX54A
T6
BC393
T7
BC394
T8
BC394
R9
270
R10
270
R11
29K
OUT
INC7
100nF
C5
1000µF
C8
100nF
C6
1000µF
C1
1000µF
C2
1000µF
C3
100nF
C4
100nF
+40V
+20V
D1 BYW98100
GND
-20V
-40V
D93AU016
Figure 18: High Efficiency Application Circuit
APPLICATION INFORMATION
HIGH-EFFICIENCY
Constraints of implementing high power solutions
are the power dissipation and the size of the
power supply. These are both due to the low effi-
ciency of conventional AB class amplifier ap-
proaches.
Here below (figure 18) is described a circuit pro-
posal for a high efficiency amplifier which can be
adopted for both HI-FI and CAR-RADIO applica-
tions.
The TDA7294 is a monolithic MOS power ampli-
fier which can be operated at 80V supply voltage
(100V with no signal applied) while delivering out-
put currents up to ±10 A.
This allows the use of this device as a very high
power amplifier (up to 180W as peak power with
T.H.D.=10 % and Rl = 4 Ohm); the only drawback
is the power dissipation, hardly manageable in
the above power range.
Figure 20 shows the power dissipation versus
output power curve for a class AB amplifier, com-
pared with a high efficiency one.
In order to dimension the heatsink (and the power
supply), a generally used average output power
value is one tenth of the maximum output power
at T.H.D.=10 %.
From fig. 20, where the maximum power is
around 200 W, we get an average of 20 W, in this
condition, for a class AB amplifier the average
power dissipation is equal to 65 W.
The typical junction-to-case thermal resistance of
the TDA7294 is 1
o
C/W (max= 1.5
o
C/W). To
avoid that, in worst case conditions, the chip tem-
perature exceedes 150
o
C, the thermal resistance
of the heatsink must be 0.038
o
C/W (@ max am-
bient temperature of 50
o
C).
As the above value is pratically unreachable; a
high efficiency system is needed in those cases
where the continuous RMS output power is higher
than 50-60 W.
The TDA7294 was designed to work also in
higher efficiency way.
For this reason there are four power supply pins:
two intended for the signal part and two for the
power part.
T1 and T2 are two power transistors that only op-
erate when the output power reaches a certain
threshold (e.g. 20 W). If the output power in-
creases, these transistors are switched on during
the portion of the signal where more output volt-
age swing is needed, thus "bootstrapping" the
power supply pins (#13 and #15).
The current generators formed by T4, T7, zener
TDA7294
10/17